Neuropathic pain is caused by damage or disease affecting the somatosensory system. It is often associated with abnormal sensations referred to as dysesthesia. These sensations are perceived by the subject as an unpleasant, abnormal sense of touch, or other sensations such as burning, wetness, itching, electric shock, and pins and needles. Neuropathic pain may also involve pain produced by normally non-painful stimuli (allodynia). Neuropathic pain may chronic and continuous and/or episodic. For example “phantom pain” from an amputated limb or from a part of the body from which the brain no longer receives signals is a type of neuropathic pain. The etiology of neuropathic pain is quite broad, and can be caused by traumatic injuries, spinal cord injury, multiple sclerosis, stroke, diabetes and other metabolic conditions, herpes zoster infection, HIV-related neuropathies, nutritional deficiencies, toxins, remote manifestations of malignancies, immune-mediated disorders and physical trauma to a nerve trunk.
Neuropathic pain is very difficult to treat. At present there is no effective treatment. Only about 40-60% of patients achieve partial relief via conventional therapies. See, for example, Dworkin R H, O'Connor A B, Backonja M, et al. (2007). “Pharmacologic management of neuropathic pain: evidence-based recommendations,” Pain 132 (3): 237-51. Thus there remains a long-felt and unmet need for an effective method to treat neuropathic pain.